This invention pertains to a process for the production of acylated 1,3-dicarbonyl compounds by rearrangement of corresponding enol esters.
The types of compounds which will be referred to hereinafter as acylated 1,3-dicarbonyl compounds have the general formula ##STR1## in which R is a group as hereinafter defined (and may generally be an optionally substituted aromatic or aliphatic moiety). Compounds of this type have been described in a number of references as being useful, for instance, as chemical intermediates and/or pesticides. The rest of the molecule, which includes the dicarbonyl group, has a generally cyclical structure.
Most preferably the cyclical 1,3-dicarbonyl group includes a 5- to 6-member ring, which may be carbocyclic or heterocyclic. 6-Membered rings are preferred.
Acylated carbocyclic 1,3-dicarbonyl compounds of this type have the general structure ##STR2## in which R is generally an optionally substituted aliphatic or aromatic moiety as hereinafter defined and n is 2 or 3, preferably 3. The ring may be unsubstituted (all X and Y groups are hydrogen), or one or more hydrogen atoms may be replaced by aliphatic, aromatic, heterocyclic or alkylene groups, preferably hydrocarbyl groups. Examples of such hydrocarbyl groups are alkyl, particularly lower alkyl, phenyl, and C.sub.2 -C.sub.5 alkylene groups such as dimethylene, trimethylene and the like, in which case the compounds have a spiro structure. Examples of other substituents include acyl, carboxyl and carboalkoxy, various substituted phenyl groups and various heterocyclic rings such as pyridyl, pyrimidyl, etc.
This class includes 1,3,5-tricarbonyl compounds; in these compounds two hydrogen atoms bonded to a single carbon atom are replaced by a doubly bonded oxygen atom.
The carbocyclic ring may be saturated or unsaturated, containing an olefinic bond linking the 4- and 5-carbon atoms.
Acylated heterocyclic 1,3-dicarbonyl compounds of this type have the general formula ##STR3## in which R is as defined herein and Z is a chain which contains 2 or 3 ring atoms, at least one of which is nitrogen, oxygen or sulfur. Nitrogen atoms in such rings may be unsubstituted or may be substituted by a C.sub.1 -C.sub.4 alkyl group, preferably a methyl group. Carbon atoms in such rings may be unsubstituted or may be substituted similarly to those in the carbocyclic compounds described above. Where possible, heterocyclic rings may be saturated or unsaturated.
Examples of heterocyclic, 1,3-dicarbonyl structures include, for instance, barbituric acid derivatives, hydroxypyrones, 3,5-dioxotetrahydropyrans and -thiopyrans, cyclical oxolactones, cyclical oxothiolactones and oxolactams.
One method for production of acylated dicarbonyl compounds is disclosed in European Patent Application, Publication No. 90262 and involves the reaction of an optionally substituted 1,3-cyclohexanedione with a substituted benzoyl cyanide. The reaction is carried out in the presence of zinc chloride and triethylamine. Such a process, however, has some drawbacks. Benzoyl cyanides are somewhat expensive reagents, and hydrogen cyanide is produced by this reaction in quantities of about one mole for each mole of acylated dicarbonyl compound. It would be desirable therefore to conduct the reaction using a less expensive and more readily available type of acylating agent which additionally did not produce such quantities of hydrogen cyanide. Benzoyl chlorides, for instance, are a relatively inexpensive and available form of acylating agent. However, benzoyl chlorides are stronger acylating agents than benzoyl cyanides and in the presence of the usual catalysts will tend not to acylate at the carbon atom between the two carbonyl groups, but rather directly attack one of the carbonyl groups itself, forming an enol ester of the type ##STR4##
It is known from a number of references that acylated cyclical dicarbonyl compounds may be produced from the corresponding enol esters by rearrangement: ##STR5## The references disclose several different types of acylated dicarbonyl compounds and various catalysts or promoters for the rearrangement of enol esters to the acylated dicarbonyl compounds.
For instance, Akhrem et al., Synthesis, p. 925-927 (1978) disclose the production of a number of acylated cyclohexanediones by reaction of 1,3-cyclohexanedione with an acylating agent (particularly an acyl halide) in two stages. In the first stage the acyl halide is reacted with the cyclohexanedione in the presence of pyridine to produce an enol ester, which is then converted to the acylated cyclohexanedione by rearrangement in the presence of a two-molar excess of aluminum chloride. Acylating agents used in this work had the formula RCOCl in which R was various alkyl (e.g., methyl, ethyl, propyl), phenyl, substituted phenyl, benzyl, and substituted benzyl groups.
Tanabe et al., Chem. Letters, p. 53 (1982) describe work on production of 3-acyl-4-hydroxy-2-pyrones by acylation of pyrones with alkyl- or alkenyl-type acyl halides and rearrangement of the enol ester formed using a catalytic amount of 4-dimethylaminopyridine.
European Patent Application (Publication No.) 123001 discloses that other aminopyridine derivatives as well as certain N-alkylimidazole derivatives are suitable catalysts for rearrangement of enol esters to acylated cyclohexanediones having a 5-carboxylate substituent.
USSR. Pat. No. 784,195 discloses rearrangement of an enol ester to produce 2-oleoyl-cyclohexane-1,3-dione in the presence of molten sodium acetate at 160.degree.-170.degree. C. European Patent Application, Publication No. 80301 discloses rearrangement of enol esters of 5-(polymethylphenyl)-1,3-cyclohexanediones to the corresponding acylated cyclohexanediones in the presence of a Lewis acid. Acylating agents used included anhydrides and acyl halides of the formula RCOCl in which R was alkyl, fluoroalkyl, alkenyl, alkynyl, or phenyl.